NEW YORK (AP).- The invitation to a 1960s "happening" was intriguing: Pay $10 to enter a lottery for the chance to get a key to a Penn Station locker containing artwork.

For one New Yorker who attended the 1965 event, the key revealed a Roy Lichtenstein drawing that Christie's auction house estimates will fetch around $1 million at its May 11 auction.

"Kiss V" is a study for one of Lichtenstein's major paintings of the same name, which is in a private collection and belongs to his dream-girl series created between 1961 and 1965. Measuring 6 inches by 6 inches, the study is a comic book-inspired close-up of a man and woman, executed in graphite and wax crayon.

The artist, who died in 1997, was famous for his cartoon-inspired style that helped launch  along with Andy Warhol, Jasper John and others  the pop art movement.

"Happenings," spontaneous and fun arts and performance events, sprung up all around the city during the heady days of the 1960s.

The March 1965 one was organized by a group of emerging pop artists. It invited participants to come to the Hotel Chelsea  home to numerous legendary writers and artists  to enter into the $10 lottery for a key to about 20 lockers at the old Penn Station, which was then being torn down.

Thirteen artists participated in the Artists' Key Club event. Besides Lichtenstein, they included Warhol, Christo and Arman.

"It was a large party for artists and people who were part of a hip downtown group having fun," said Christie's postwar and contemporary art expert Brett Gorvy. Later, he said, the group partied at a restaurant on the proceeds from the event.

Participants did not know which key opened which locker. And not everyone was as lucky as the woman who claimed the Lichtenstein drawing.

"One artist put up a group of very pungent cheeses" for his conceptual piece and another "had spices and herbs as his art work," said Gorvy.

In 1965, the Lichtenstein drawing would probably have been valued at about $50. The current owner, who declined to be identified, decided to sell it because she had it recently appraised and was shocked to find out how much it was worth, Gorvy said.

Gorvy said Lichtenstein's "Crying Girl," a drawing of similar size and from the same series, sold at Christie's in 2007 for $1.7 million. He said he expected "Kiss V" to surpass its pre-sale estimate of $800,000 to $1.2 million because of its unique provenance.

Lichtenstein was a "marvelous draftsman, who took the comic image and made it very much his own," said Gorvy.

The auction record for Lichtenstein is $42.6 million for his "Oh ... Alright," a comic book image of a forlorn woman clutching a telephone. It sold at Christie's in November.